DaTscan (Ioflupane I 123 or phenyltropane) (GE Healthcare) is a radiopharmaceutical contrast agent recently approved by US FDA for use with single-photon emission computed tomography (SPECT) for detecting dopamine transporters (DaT) in suspected Parkinsonian syndromes.
In January 2011, FDA approved DaTscan for non-invasive visualization of striatal DaT while differentiating between essential tremors and tremors due to Parkinsonian Syndrome (which includes idiopathic Parkinson’s disease, multiple system atrophy and progressive supranuclear palsy). DaTscan cannot help in differentiating among the different manifestations of Parkinsonian syndrome. DaTscan is an adjunct to other diagnostic evaluations.
Dopamine is one of the main monoamine neurotransmitters in the brain and is involved in the regulation of important brain functions such as locomotor activity, reward, and cognition. DaT is a plasma membrane protein expressed exclusively in dopamine neurons, where it acts by rapidly clearing dopamine released into the extracellular space, thus regulating the amplitude and duration of dopamine signaling.
DaTScan binds to the dopamine transporters in the brain and thus helps in their visualization. The pathology of Parkinson’s disease consists of the loss of dopamine neurons in the substantia nigra and the reduction of dopamine projections to the striatum. The DaTScan image of Essential Tremor shows normal distribution of DaT whereas there is asymmetric loss of DaT in Parkinsons Disease.
How is it being used?
- To differentiate essential tremor from tremor due to parkinsonian syndromes, including idiopathic Parkinson’s disease, multiple-system atrophy, and progressive supranuclear palsy, as an adjunct to other diagnostic modalities.
- DaTScan combined with a second scintigraphy can be useful in evaluating other neurodegenerative diseases such as Lewy-body dementia (DLB) or multiple system atrophy. It has been recommended that low DaT uptake in the basal ganglia, as shown by SPECT imaging, should be considered a suggestive feature of diagnosis of DLB. It is being studied as a technique to help in the differentiation of Alzheimer disease from DLB.
- It is also being studied for its action as a biomarker for evaluating the disease progression.
- Till now, DaTScan has led to controversial results in diagnosing Attention Deficit Hyperactivity Disorder (ADHD).
The FDA and future outlook
DaTScan was approved for use in Europe in year 2000. US FDA has approved its use in January 2011. FDA approved DaTScan on the basis of two phase 3 clinical trials.
Some members voted against the approval. They do not want to make DaTScan as the gold standard assay for diagnosing Parkinsons Disease. The persons who voted against the approval of DaTScan thought that the benefits of DaTScan in management of the Parkinson disease have not been proved. Some stressed that DaTScan is not cost-effective.
Adverse reactions such as headache, nausea, vertigo, dry mouth, and mild to moderate dizziness have been reported. In postmarketing experience, hypersensitivity reaction and injection site pain have been reported. DaTScan emits gamma radiation and must be handled with safety measures.
A thyroid-blocking agent should be given at least one hour before the dose of DaTscan. SPECT imaging should be started between 3 and 6 hours post-injection. The recommended DaTscan dose is 111 to 185 MBq (3 to 5 mCi). It is possible to obtain diagnostic DaTscan images using 180 degrees acquisition in difficult patients. The total length of the scan may also be shortened by half using L-mode or V-mode camera head configuration.